The use of wireless communication systems is growing with users now numbering well into the millions. One of the popular wireless communications systems is the cellular telephone, having a mobile station (or handset) and a base station. Cellular telephones allow a user to talk over the telephone without having to remain in a fixed location. This allows users to, for example, move freely about the community while talking on the phone.
Cellular telephones may operate under a variety of standards including the code division multiple access (CDMA) cellular telephone communication system as described in TIA/EIA, IS-95, Mobile station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System, published July 1993. CDMA is a technique for spread-spectrum multiple-access digital communications that creates channels through the use of unique code sequences. In CDMA systems, signals can be and are received in the presence of high levels of interference. The practical limit of signal reception depends on the channel conditions, but CDMA reception in the system described in the aforementioned IS-95 Standard can take place in the presence of interference that is 18 dB larger than the signal for a static channel. Typically the system operates with a lower level of interference and dynamic channel conditions.
A CDMA base station communicates with a mobile station with a signal having a basic data rate of 9600 bits/s. The signal is then spread to a transmitted bit rate, or chip rate, of 1.2288 MHz. Spreading applies digital codes to the data bits, which increase the data rate while adding redundancy to the CDMA system. The chips of all the users in that cell are then added to form a composite digital signal. The composite digital signal is then transmitted using a form of quadrature phase shift keying (QPSK) modulation that has been filtered to limit the bandwidth of the signal.
In a code division multiple access (CDMA) spread spectrum communication system, a common frequency band is used for communication with all base stations within that system. If two or more mobile users simultaneously contend for an idle packet-data channel in a system using IS-707, the system will only allow one access to the channel. Mobile users unsuccessful at accessing the channel must repeat the transmission of the data packet until it is accepted by the system. The system users transmitting data packets to mobile users also contend for the downlink by being placed in a queue.
Under the current IS-707 standard, when a system user is unable to access the channel, the system user reattempts connection after a predetermined wait. The length of the wait is defined by the IS-707 standard, and is the same for each system user. After each subsequent unsuccessful attempt to connect to the system, the length of the wait is increased until a maximum value is reached. However, if the system users were denied access to an idle channel because multiple users attempted to simultaneously access the channel, each user will attempt to re-access the channel at the same time, causing further collisions.
What is needed is a system that allows the system users to wait for a free channel to connect to the system while reducing the probability of reconnection collision with other system users.
The present invention is a system for distributing the reconnection attempts of multiple system users in a CDMA telephone system over a broad time window. The present invention allows either the base station or the mobile station to process data to determine an appropriate reconnect time. The data may include resource capability, priority, client connects pending, and timing and amount of data on pending connection requests. Using this data information, a more efficient reconnection scheme may be developed. Under an intelligent reconnection scheme, the probability of system users attempting simultaneous reconnection is reduced, thus reducing the likelihood of reconnection collision.
One aspect of the invention is a method of determining the length of time between connection requests in a wireless communication system. The method comprises collecting data regarding connection requests and calculating reconnection timing for each connection request based on the collected data. The method may further comprise transmitting the collected data or a subset thereof to a mobile station. The collected data comprises, among other things, an amount an distribution of connection requests, a number of available resources, an expected duration of a connection, an expected duration of current connections, a priority indicator of the connection requests, and an expected number of new connection requests.
Another aspect of the present invention is a timer setting circuit for use in a mobile communication system. The timer setting circuit comprises a reconnection timer and a timer setting circuit. The timer setting circuit sets the reconnection timer to a value after a failed connection attempt between a mobile station and the mobile communication system. The timer setting circuit determines the value of the reconnection timer is based on a set of data regarding connection requests.
Another aspect of the invention is a method of intelligently managing the reconnection timing in a wireless communication system. The method comprises determining a number of available resources and estimating an expected release time of unavailable resources. The method further comprises determining the number of refused connection attempts and calculating a reconnection timing for each of the refused connection attempts based on the number of available resources and the expected release time of unavailable resources. The method further comprises establishing a priority of each of the refused connection attempts and adjusting the reconnection timing for each of the refused connection attempts based on the priority.
Another aspect of the invention is a mobile communication system comprising a transceiver and a reconnection control device. The reconnection control device determines the timing of a connection attempt between a mobile station and the mobile communication system. The reconnection control device determines the timing based on a set of data regarding connection requests. The set of data may include, among other things, an-amount of connection requests, a number of available resources, an expected duration of a connection, an expected duration of the current connections, a priority indicator of the connection requests, and the expected new connection requests. The reconnection control device may be located within a base station or a mobile station.
Another aspect of the invention is a mobile communication system in which the base station can efficiently manage contention of a common access resource. The access resource is shared and is not dedicated to a particular mobile station. Therefore, even if multiple traffic channels are free, the mobile stations are not requesting the resources at the same time.